1. Field of the Invention
The present invention relates to discovery and location systems, and more particularly relates to a location device which uses orbiting global positioning satellites (GPS) to determine a location and which is capable of transmitting a location (longitude and latitude) to search and rescue authorities.
2. Description of the Prior Art
In the United States, the U.S. Air Force Rescue Coordination Center (AFRCC) is responsible for coordinating search and rescue efforts. An activities report, issued by the AFRCC, indicates that a major problem in rescue missions was the high rate of false signals transmitted by Emergency Locator Transmitters (ELTs) used to locate aircraft and marine vessels in distress. Due to the high rate of false signals, search and rescue authorities may not be immediately dispatched upon receipt of a distress signal unless substantial additional evidence exists to confirm the emergency. This delayed reaction could mean life or death to those stranded in severe conditions on land or water.
Thus, there is a need for a device that can quickly and reliably determine its location and relay that information to search and rescue authorities. The device must be able to utilize existing satellite services available to the general public. Various prior art systems have been developed to send a tracking signal to a receiving station, each having disadvantages as discussed below.
For example, U.S. Pat. No. 3,063,048 to Lehan, et al. discloses a system that utilizes an orbiting satellite to discover and determine the location of an object whose position on the earth's surface is unknown. The disclosed system utilizes a Doppler frequency shift algorithm to determine the object's position. The system as disclosed is outdated, impractical and expensive to implement. Furthermore, this type of system is inaccurate compared to presently available location determination systems.
U.S. Pat. No. 5,223,844 to Mansell, et al. discloses a vehicle tracking and security system that utilizes GPS position signals. The vehicle unit includes a GPS receiver for determining a location of a vehicle. The vehicle unit also includes a controller, responsive to the satellite receiver, for transmitting information onto a communications link. The information includes an alarm event identification and the vehicle location. Although the patent states that this system is suitable for use in fleet vehicle management, vehicle theft deterrent, stolen vehicle tracking, railroad car tracking and so forth, the system is not designed to reliably transmit rescue signals or to be portable, nor is it designed for use in harsh environments such as at sea or in aircraft. Furthermore, the system is complex having many components mounted within a vehicle and cannot be carried by a person for use in an emergency situation involving an aircraft or a marine vessel.
U.S. Pat. No. 4,813,025 to Rowland et al. discloses a system for locating a person who has fallen overboard from a ship. The system utilizes both radio and ultrasonic signals to transmit distress signals to an ocean vessel having suitable receiving equipment. This type of system does not utilize global positioning satellites and is not capable of providing specific location information to a distant receiving rescue station. More specifically, the system is limited to transmitting a distress signal from a person in distress to a properly equipped vessel within a very close distance.
A location signalling device for automatically placing a radio distress call is described in U.S. Pat. No. 5,193,215 to Olmer, et al. The disclosed device receives positional data from either a manual keyboard input entered by the operator or by a special interface to external positioning equipment (i.e. LORAN or GPS receiver). The rescue signal is transmitted upon activation by the operator using a VHF/SSB radio transmitter that is also external to the device. The device is difficult to use in most emergency situations due to dependence on external devices to provide both positional data and signal transmission capability. More specifically, in emergency situations, crews abandoning a quickly sinking boat or aircraft may not have sufficient time to program the system with the correct information and begin transmission of the rescue signal. Furthermore, there is no total system operation verification to ensure that the GPS receiver and rescue message transmitter are operable. The rescue signal would be also restricted by the range limitations of the VHF/SSB radio frequencies. A rescue device for general aviation and marine use needs to be portable, reliable and not dependent on external devices to operate.
In the foregoing prior art disclosures, the systems described are generally costly, complicated to develop, not portable and are limited by the technology selected to relay the distress signal to search and rescue authorities. Thus, there is a need for an emergency locator system which is portable and combines the use of existing GPS and communications satellites for accurate, reliable, trouble-free transmission of rescue signals to the authorities to expedite rescue missions.